Railroad hopper cars typically include an underframe for supporting a walled enclosure in which lading is held and transported. As is conventional, the underframe of the car is supported toward opposite ends by well known wheeled trucks which ride on tracks or rails. The bottom of the walled enclosure is usually provided with two or more individual discharge openings for allowing the lading to be discharged from the walled enclosure. The walled enclosure furthermore typically includes sloped or slanted walls or sheets extending upwardly from a periphery of each opening to promote gravitational movement of the lading toward the opening.
Various methods and devices are known in the art for individually closing the discharge openings in the walled enclosure. Basically, such closure devices or gate assemblies are divisible into two categories. Some hopper cars utilize a sliding door or valve type system for selectively opening and closing the openings at the bottom of the walled enclosure. Alternatively, some hopper cars are provided with pneumatically enabled discharge systems which rely on a pressure differential system for exhausting particulate matter or lading from the enclosure of the hopper car.
A conventional slide gate system includes a frame which is bolted or otherwise secured to the hopper car. The frame likewise defines a discharge opening arranged in registry with the opening at the bottom of the slanting walls on the hopper car. A gate or door is arranged on the frame for sliding movement along a generally horizontal path of travel between open and closed positions relative to the discharge opening on the frame of the gate assembly. A door operating mechanism including one or more racks, typically secured or attached to the door, and rotatably driven pinions is typically used to slide the door between open and closed positions. In an open position, the door of the gate assembly permits the contents of the hopper car enclosure to pass gravitationally from the walled enclosure and through the discharge opening defined by the gate assembly. In a closed position, the door extends across the discharge opening on the frame to shut off the material or matter flow through the gate assembly.
A conventional pneumatic discharge system for hopper cars involves connecting a discharge assembly including a pan-like housing beneath each opening in the bottom of the hopper car. A pneumatic discharge conduit extends from at least one of the sides the pan-like housing in a direction generally normal to a longitudinal axis of the car. One end of the pneumatic conduit opens to the interior of the pan-like housing while an opposite end is adapted for connection to a suction hose or the like for conducting the lading held and stored within the walled enclosure to any suitable discharge station.
The transportation and unloading of finely divided materials, and particularly food stuffs, such as sugar, flour and the like within and from the walled enclosure of the hopper car exacerbates the problems involved with the design and engineering of a railroad hopper car discharge gate assembly. When the lading to be transported involves food stuffs, the FDA has promulgated certain rules and regulations which must be met in order for the hopper car to qualify for transporting food stuffs. Of course, one of the paramount concerns involves designing the hopper car discharge gate assembly such that no foreign matter, accumulation of moisture, or insect infiltration is permitted to contact and possibly contaminate the food stuffs even while they are being discharged or unloaded from the railway hopper car.
Sliding gate closure systems have proven adequate over the years. There are, however, problems inherent with these designs. It is common practice to load a hopper car through roof hatches. The lading, when initially introduced into the walled enclosure, is mixed with air and is very fluid. After standing and as the car travels, however, the lading loses the air film from the finely divided particles and the lading settles and becomes very compact.
As mentioned, the discharge gate assembly is mounted at the bottom of the walled enclosure and, in sliding gate systems, the door must be slidably moved against the friction imposed thereon by the load. Known slide gate systems for hopper cars have relatively large doors to effect discharge of the lading in a timely and efficient manner. Once the door has begun movement, it can be moved through its path of travel with a reasonable amount of torque or input to the door operating mechanism. At the onset of door travel toward an open position, however, such sliding gate systems require a relatively high initial opening force to be imparted to the door.
In those hopper cars which transport food stuffs and utilize a sliding gate for controlling the discharge of lading from the walled enclosure of the hopper car, the frame of the gate assembly is usually equipped with a flanged skirt depending from and arranged in surrounding relation relative to the discharge opening defined by the frame of the gate assembly. The flanged skirt defines a discharge plenum. Typically, an air sled or other form of unloading apparatus is clamped to the flanges on the skirt during a discharge operation thereby permitting the food stuffs in the enclosure of the hopper car to be discharged directly and protectively into the sled and, thus, conveyed away from the hopper car. To inhibit debris, insects, moisture, clay and other forms of debris from contaminating the underside of the door and interior of the discharge plenum during transport of the hopper car, such sliding gate systems typically include a sanitary plate or cover plate which slides between open and closed positions in a horizontal plane generally parallel to the door to close the discharge plenum and protect the underside of the door during transport of the hopper car. Of course, known sanitary plates or cover plates are neither designed nor configured to withstand the load which can be placed thereon by the commodity in the enclosure of the hopper car.
Another problem has been identified with sliding gate systems when the lading in the walled enclosure involves fine granular food stuffs. As will be appreciated, to enable the sliding door to operate between positions, an operating gap or opening must be provided between the frame of the gate assembly and the door. Such gap or opening is typically provided between the skirt on the frame and the door. It is through this opening that contaminants, moisture, and related debris can enter the discharge plenum, thus, contaminating the food stuffs upon discharge of the lading from the hopper car and through the discharge plenum.
Arranging seals or gaskets about the discharge opening of the gate assembly frame in an attempt to close or seal such openings has often resulted in the seal or gasket being pulled from the gate assembly. The racks on the door coupled with the sliding movement of the door between open and closed positions further complicate the ability to seal the door against contaminants passing into the discharge plenum or opening on the frame of the gate assembly. Moreover, the required need to seal an element of the gate assembly movable in opposite linear directions furthermore complicates the sealing ability of the gate assembly.
It is known in the art to mount a pan-like structure or housing including the pneumatic discharge conduit to the frame of the gate assembly beneath the sliding door. The pan-like structure or housing is typically fastened to the walled enclosure of the hopper car beneath the sliding door with a plurality of fasteners. As such, the hopper car can function in either a gravitational discharge mode or a pneumatic discharge mode. Of course, valuable time is consumed and lost by affixing and removing the pan-like housing from the hopper car depending upon which type of discharge operation is required or desired. Mounting and arranging the pan-like structure or element above the sliding door of the gate assembly has been found to obstruct the flow of material from the walled enclosure in a gravitational mode of material discharge. Moreover, it is desirable to provide only a single drive mechanism for operating the components of the gate assembly thereby simplifying its operation.
Thus, there remains a need and a desire for a gate assembly for a railroad hopper car which can be conditioned for either pneumatic or gravitational discharge of lading from the walled enclosure of the hopper car and which utilizes but a single operating mechanism for operating the components of the gate assembly in timed relation relative to each other. Moreover, it is desirable to provide a gate assembly for a railroad car having a sliding door and wherein the operating mechanism imparts a high impactual opening force against the door during initial stages of its movement toward an open position. Additionally, there is a need and desire for a gate assembly for a railroad hopper car including modular components permitting the gate assembly to be easily and readily conditioned for pneumatic and/or gravitational discharge or gravitational discharge only simply by interchanging the components thereof.